Let's start out with the Teleological Argument.
Teleology: the philosophical study of design and purpose. The supposition that there is purpose or direction in the works and processes of nature.
Teleological Argument: the Argument from Design: argues for the existence of god or a creator based on perceived evidence of order, purpose, design or direction in nature.
Here's the basic argument:
- The universe is too complex, orderly, adaptive, apparently purposeful or beautiful to have occurred randomly or accidentally.
- Therefore the universe must have been created by a sentient, intelligent, wise or purposeful being.
- god is a sentient, intelligent, wise or purposeful being.
- Therefore god exists.
You can substitute just about anything in for the universe. The eye, humans, the fundamental constants of the universe, etc.
Many great men have used this argument over the centuries, but that doesn't make it valid. Socrates, Plato, Aristotle and Cicero to name a few. Cicero started the Watchmaker Analogy:
"When you see a sundial or a water-clock, you see that it tells the time by design and not by chance. How then can you imagine that the universe as a whole is devoid of purpose and intelligence, when it embraces everything, including these artifacts themselves and their artificers?" (Cicero, De Natura Deorum, ii. 34)